Don't compare yourself to others:
No matter at what level you are as a musician, there will always be someone – if not many – who will be able to dazzle you with their musical knowledge. I used to let it depress me but I realized that when I let that happen I stopped learning for awhile. I became un-teachable.I don't hold this exactly true for all things but a person I respect once said to me. "If you can't explain it, you don't understand it." Well I would say it differently. The more you teach it, the better you learn it.
There is so much I don't understand about musical theory but there is a level in my experience and training where I understand intuitively. That's where you will really know it when you use it. I use much of the theory I know without fully understanding it.
As I have matured as a musician, I have come to gradually understand better what I "knew" in my playing. It's like the difference between playing by "ear" and being able to sight read from a chart for your instrument.